Why Is a Secondary Immune Response Stronger

Why is a secondary immune response stronger?

A) Exposure to a previously encountered antigen gives rise not only to effector cells but also to clones of long -lived memory T cells and memory B cells.
B) Antibodies produced during the primary response are still present circulating in the blood.
C) Body cells develop resistance to the pathogen.
D) Body cells are primed to produce antibodies against the pathogen.
E) Effector cells produced during the primary response are still present circulating in the blood.